TK75 vs BTU Shocker - Let the battle begin! (NEW UPDATE ON POST 125)

Glenn, That’s bad!!! hehehehe :smiley:

The TK75 isnt driven at under 3a per emitter. No way. You don’t get 975otf at under 3a with a U2. Not gonna happen. At the emitter - sure, not otf. Possible put on a big slab of copper it might come close, but not in a triple led setup in a under $200 light like the TK75. It’s not gone to happen. The TK75 is driven somewhere in the 3.5-3.8a range. I’ve got U2’s and U3’s driven just slightly over 3a and they fall about 100otf short of that. I’ve got U3’s driven at 3.75a on copper pills that are almost there with about 960otf at 30sec.
But U2’s, triple setup, UNDER 3a per LED, in a factory setup, putting out 975otf each - nope.

I’m 146kgs. Guess I’m in the other 10% bracket.

How long does the BTU run of high before it’s too hot?

Truthfully I don’t know. I’ve generally used the BTU’s turbo in lots of short bursts of under 1 minute. I know even while doing a lumen test in my lightbox with foam around its head (for light sealing) the light isn’t remotely starting to heat up in those 40 sec or so. The head isn’t warm at all. And I don’t feel it’s due to lack of heatsinking because the lumen output levels off very nicely, with only a slow drop after about 5-10sec.
I wouldn’t hessitate to run it on turbo well after the 3 min. kickdown. Kicking back on multiple times would likely be ok. Thats one place this lights big beefy body helps by lots of mass to absorb the heat the LED’s generate. I do need to experiment more with longer runtimes and see how it does.

Someone have already measured TK75 using power supply, at 7.5V, current draw is about 4A. That is 30Watt. If it is 100% efficiency which is impossible, each LED get 10Watt. XML driven at 3A typical voltage is 3.35V, and that is about and above 10W. So no way TK75 is driven above 3A per led. Based on this and runtime, I estimate it is 2.8A per led. XML maximum limit is 3A, no way a reliable brand like Fenix will drive it above 3A. Fenix will prefer to make it perfect in heatsink, and drive it below 3A. That is what has happened in TK75. Fenix is always playing safe. TK70 is 2.5A per led. With smaller head, it is not logical for Fenix to drive TK75 to be 3.5A per led.
About your last line about 975otf per led, maybe you have overestimated the otf. Fenix official number is 2600 lumens, that is way too low compare to your number.

The TK75, while impressive, cannot bend the laws of physics.

It is logical for Fenix to run a LED slightly over the 3amp for turbo modes. A XML driven at 3.5a or even more is very safe if it has any heat sinking at all. Also there has been many reports that TK70 are actually in the 2500-2600otf range. I have never tested one so I cannot say yeah or neah on that.
As for my numbers, I know my lightbox reads true for lights up to 2500 otf. I have tested multiple of them, such as two SRK’s. One tests out as 2180otf and one tests out at 2200otf, both pretty much what everybody expects them to put out. I have even sent lights to other members to verify my numbers. And we have always been with in a few percent of each other.
I haven’t tested anything over 2500 lumens before these two lights, but there is no logical reason to think my numbers would get off by 3-400 lumens when testing lights just slightly more powerful the Kings. Sure I could be off a few percent, my lightbox and meter setup is good, but not perfect. But it’s not 300 lumens off.
The Fenix TK75 is driven over 3 amps on turbo. I have no doubt.

3.5A will be way over 30W. Maybe Fenix manage to break law of physics.

Not sure if we are talking bout the same thing… My Btu on turbo

Dale, It is same thing if your picture is about current flow into led. If yes, BTU is indeed driven to 3.8A according to your picture. The issue is BTU is not performing as it should be. It is just shortening led and battery life in turbo mode with high current consumption if compare to Fenix TK75.

TK75 is not driven above 3A according to Fenix runtime and also wattage measurement I attached below. At 7.5V, total wattage is about 30W.
If TK75 is driven to 3.5A per led according to rdrfronty, it will be about 12W per LED, and it will be 36W for 3 LED alone. If we add in efficiency into calculation, it will be about 38-40W. If only Fenix manage to get the extra 10W out of thin air since they manage to break laws of physics.

Don’t mean to trash BTU, by itself it is very good flashlight if not looking at the lens, reflector and battery carrier. Problem is relatively TK75 is too good until rdrfronty think it is driven to 3.5-3.8A. Which is not true.

According to reviews I’ve seen, the TK75 puts out 41wt. And where are you getting 7.5V? The voltage is 8.4, not 7.5V.

The TK75 is driven at a minimum of 3.5a on turbo. Also the photo of dales BTU has been ramped up slightly. Stock is closer to 3.8 vs his 3.9+ amps.
The BTU is running just as efficient as the TK75 give or take a couple percent.

Just look at the graph I posted. Voltage at 7.5V, current is about 4.05A. It is 30W.
Can you post the link of the review? Wish to see which genius did that review.

Yes I can. And it’s not 7.5v. I don’t know where you come with a voltage like that with 4.2v batteries. You can only have 4.2, 8.4, 12.6, and 16.8v. And with its configuration, the voltage is 8.4.

Good that you are standing firm to what you believe in.

Well, heck. Your graph you posted shows I’m right. It shows peak voltage at 8.4. And it shows the amps at 3.5a per emitter.

I love my BTU. Wouldnt trade it. I see a few areas where there could be a bit of improvement. To be honest there are no perfect lights. Lest we would all only own one. I will say this. My BTU with the XML 2 U2 with the driver boosted a bit. Is a world of difference from the CW’s it came with. I like to poke fun a the TK75 users. But the TK is a excellent light as well… Now the technical aspects I leave to you fine people.

That reviewer made a very big mistake not taking battery voltage sag into his calculation.
He measure tail cap current of 4.9A, and he assume voltage of 8.4V, and get a 41.16Watt. This is completely not true as it won’t be 8.4V.
Since he made such a mistake, I doubt his measurement of 4.9A either as high current measurement is not as simple as it looks.
When it comes to wattage measurement, you better believe in power supply that has +/-sense connection. Wattage measurement using batteries has too much variable in it depending on your batteries condition and cables.

That is volt-current graph of whole torch. Not the led alone. No one can put 8.4V between led and not burning it.